Exocytosis of neurotransmitters, hormones and other cell secretory products is believed to occur by calcium-dependent movement of the assembled secretory vesiole to the cell surface and subsequent fusion of the secretory vesicle with the plasma membrane. Our special interest has been to understand the processes of granule assembly, movement, contact and fusion. We have discovered that catecholamine entry into mature chromaffin granules is ATP dependent but occurs by exchange for endogenous catecholamines. We have also found that the molecular species entering the granule is neutral, rather than the commonly assumed cationic species, by using our newly synthesized quaternary catecholamine analogue, dimethyledrenaline. In this regard, catecholamine transport by the plasma membrane and the granule membrane is quite similar. The biosynthetic enzyme for adrenaline, PNMT, has been found to be induced by glucocorticoids in chromaffin cell cultures. A typical glucocorticoid receptor has been detected and quantified in chromaffin cell cytoplasm. The interaction of F-actin and chromaffin granule membranes, previously discovered by us, has now been found to be regulated not only by calcium, but also by MgATP. The mechanism involves an actin-stabilized granule membrane ATPase. Synexin, a 47,000 kd calcium binding protein that causes membrane fusion, has been studied in detail by monoclonal antibody methods. Different antibodies specifically regulate synexin self association as well as granule aggregation, sensitivity to phenothiazines and fusion by arachidonic acid. An antigenically related 67,000 kd. calcium dependent membrane binding protein that also competively inhibits synexin activity has been isolated and named synhibin. Ascorbic acid transport has been found to be sensitive to corticosteroids, and to be secreted by depolarized chromaffin cells in a calcium-specific manner, from a non-vesicular compartment.